1. Field of the Invention
This invention relates to a vertical heat treating apparatus used in a diffusion process and/or a film formation process for manufacturing semiconductor devices.
2. Description of the Related Art
Vertical heat treating apparatuses, which have recently been used in a diffusion process and/or a film formation process for manufacturing semiconductor devices, have begun to be used in a ductless atmosphere and to be reduced in floor space.
The vertical heat treating apparatus of this type has an evenly heating tube, a heater, a heat treating furnace made of heat insulting material and vertically provided in a casing. In the lower portion of the casing is mounted a vertical moving mechanism (boat elevator) for loading/unloading processing members (wafer boats) on which semiconductor wafers as articles to be processed are mounted.
Some vertical heat treating apparatuses each have a transport device for transporting wafers from transporting members (wafer cassettes) which transport the wafers to the processing member.
The use of such a vertical heat treating apparatus makes the floor space smaller than a vertical heat treating apparatus, and the loading/unloading of wafers, which is easily performed in a non-contacting state of the wafers with a reaction tube in the furnace, renders the interior of the furnace dustless.
However, there is a tendency that the diameter of semiconductor wafers has become larger and larger while the circuit pattern of semiconductor devices has become finer and finer. It is requested, therefore, that vertical heat treating apparatuses ensure that dust is prevented from being attached to articles to be processed so as to give a high yield, and their floor space be made as small as possible even though wafers to be processed have a large diameter.